Estimating the sensitivity of stomatal conductance to photosynthesis: a review

A common approach for estimating fluxes of CO 2 and water in canopy models is to couple a model of photosynthesis ( A n ) to a semi‐empirical model of stomatal conductance ( g s ) such as the widely validated and utilized Ball–Berry (BB) model. This coupling provides an effective way of predicting transpiration at multiple scales. However, the designated value of the slope parameter ( m ) in the BB model impacts transpiration estimates. There is a lack of consensus regarding how m varies among species or plant functional types (PFTs) or in response to growth conditions. Literature values are highly variable, with inter‐species and intra‐species variations of >100%, and comparisons are made more difficult because of differences in collection techniques. This paper reviews the various methods used to estimate m and highlights how variations in measurement techniques or the data utilized can influence the resultant m . Additionally, this review summarizes the reported responses of m to [CO 2 ] and water stress, collates literature values by PFT and compiles nearly three decades of values into a useful compendium.